Gas tank extension



FIG. 1 is a perspective view of the gas tank extension thereof;

FIG. 2 is a rear view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a bottom view thereof;

FIG. 7 is a top view thereof. 

The ornamental design for a gas tank extension, substantially as shown. 